From eight words a minute to 13 terabits per second in 150 years

IEC first President Lord Kelvin was central to the success of the first fully working transatlantic telegraph cable

By Morand Fachot

Given today’s low-cost or free crystal-clear voice calls and the real-time transfer between continents of vast volumes of data, including multimedia content, it’s easy to forget that just 150 years ago it took nearly two weeks for news from London to reach New York. The laying of the first fully working transatlantic telegraph cable from Ireland to Newfoundland cut that time to a few hours. IEC first President Lord Kelvin played a key role in the success of the project.

An ancient quest for fast transmission of news

Since time immemorial, men have felt the need to share critical or momentous news as quickly as possible with others in distant locations. Legend has it that in ancient Greece, news of the Greek victory over an invading Persian army, in Marathon in 490 BC, was brought to Athens by a runner who died shortly after completing a run of over 42 km (26 miles).

Ancient Greece also provided the setting and the starting point for the homing pigeons which were sent to villages at the end of each Olympic Games to announce the winners. This allowed villagers time to prepare a fitting welcome for their local heroes on their return.

Homing pigeons have been used to convey news in many civilizations throughout history. Examples include a regular service between Baghdad and Syria from the late 12th century to the late 13th century, and the news of the defeat of Napoleon in Waterloo sent to London in 1815. In the 20th century, all belligerents made extensive use of homing pigeons. The American Expeditionary Forces reportedly had more than 10 000 pigeons in service at the end of the first world war. The US Army was still training homing pigeons in the Second World War and the Swiss army disbanded its homing pigeons’ unit as late as 1994.

In some countries, in the late 18th century, messages delivered by men on horseback and homing pigeons started to be complemented by technical means. Semaphore signalling was a mechanical telegraph system using visual signals. However, it required a comprehensive infrastructure and was mostly useless in poor weather and at night.

Electrical telegraph provided more reliable and quicker news

Following a series of discoveries and inventions in the electrical domain, various telegraph systems started to be developed in both Europe and across the Atlantic in the first half of the 19th century. These experiments culminated in the development of the Morse electrical telegraph, which used a special code to transmit letters and numbers. Telegraph landlines soon criss-crossed countries and continents. The US west and east coasts were connected via overland Morse telegraph lines in 1861.

Successive technical achievements led to efforts to overcome another major obstacle: connecting countries and continents separated by sea. Initially, the main technical challenge was to reinforce and insulate underwater cables to protect them and to prevent current from leaking into water. This was achieved using gutta-percha, a form of latex produced from the sap of trees found in Southeast Asia, to coat iron-reinforcing wires protecting the copper conductor.

This allowed the first undersea cable to be laid between England and France in 1850. It was followed by more connections linking England with Ireland, Belgium and the Netherlands.

The next frontier, crossing the Atlantic

Soon after the first undersea cable was laid, a number of individuals, including the prime mover behind the project, New York businessman and financier Cyrus Field, proposed laying a transatlantic cable between Ireland and Newfoundland in 1854. They formed the Atlantic Telegraph Company in November 1856 to launch and exploit a commercial transatlantic telegraph cable.

In December 1856, IEC first President, William Thomson, Lord Kelvin, was appointed as an unpaid scientific adviser to the board of directors of the company.

The transatlantic cable idea was put to the test. The third attempt to link both sides of the Atlantic met with success in 1858 when, in mid-Atlantic, two ships connected the cables they carried before sailing respectively to Ireland and to Newfoundland.

The first transatlantic message, a 99-word telegram from Queen Victoria to US President James Buchanan, was sent on 16 August 1858. It took 16 hours to send (two minutes per letter…)

However, the cable was operational for just three weeks and provided a very weak signal. To boost this weak signal, the Atlantic Telegraph Company’s chief electrician, Edward Whitehouse, proposed increasing the voltage. Thomson opposed the idea, thinking that this would fry the cable. Whitehouse applied higher voltage shocks to the cable which eventually failed. However, evidence suggests that the poorly manufactured and damaged cable would, in any case, have failed within weeks, even without the application of the higher voltage.

Lord Kelvin’s contribution

Mentions of Thomson’s contribution to the transatlantic cable venture are often restricted to his development of two instruments central to the project: the mirror galvanometer and the syphon recorder. However, as early as October 1854, Thomson was delving into the theoretical issues facing a future transatlantic cable. By December 1854, he had laid out an entire mathematical theory explaining, in letters sent to fellow mathematician and physicist George Stokes, how a pulse of electricity travelled in an insulated submerged wire.

In his letters Thomson also analyzed the data rate that could be achieved and explained the feasibility and economic consequences of completing a transatlantic cable.

Thomson conceived a complete system for submarine telegraphy. His plan focused on adapting the Morse code for submarine work and detecting weak telegraph signals.

To achieve the latter, he developed, between 1856 and 1858, a highly sensitive instrument designed to detect the smallest possible electrical signal: the mirror galvanometer.

This was the first instrument that enabled long submarine cables to be used and made it possible to realize transmission speeds five or six times those achievable with any other instrument.

Between 1856 and 1866, Thomson personally took part in each of the major transatlantic cable expeditions: one in 1857, two in 1858, one in 1865 and the round trip in 1866 where a new cable was laid and the 1865 cable was completed.

Following the failure of the 1858 cable, Thomson made recommendations for the design and manufacture of submarine cables, which included requirements for the conductivity of the copper core, the size of the conductors and the insulation. He also stressed the importance of "systematic and searching tests for the purity and conductivity of the copper" and of control in the manufacturing process.

Thomson was knighted by Queen Victoria in 1866 for his work on the transatlantic telegraph project.

In 1870 Thomson devised the syphon recorder, the first instrument used on long cables to record the received signals.

Later, he also designed the first modern deep-sea sounding machine for assessing the depth of water, an essential piece of equipment when laying submarine cables. His Kelvite Mark IV Sounding Machine, developed with the Royal Navy between 1903 and 1906, was still being produced with only minor modifications in the 1960s.

Laying the 1866 cable

Following the 1858 setback and delays resulting from the US civil war (1860-1865), there was an eight year gap before another attempt was made in 1866.

The cable was laid by a single ship, the Great Eastern, itself an engineering feat of the time. Designed by the renowned English engineer Isambard Kingdom Brunel to carry 4 000 passengers, this ship, powered by five steam engines and sails, was launched in 1857.

She was converted to a cable laying ship in 1865 and laid her first transatlantic cable (which snapped and was lost) in July 1865.

Exactly a year later, Great Eastern successfully brought another cable on shore in Newfoundland on 27 July and the first message from England, informing that "A treaty of peace has been signed between Austria and Prussia", was received the following day.

A few weeks later Great Eastern grappled the cable lost in 1865 from the bottom of the sea, it was spliced to a new cable onboard the ship and brought to shore, providing a second connection between Europe and North America in September 1866.

At eight words a minute, the transmission speed of the 1866 cable was markedly better than that provided by the 1858 cable.

Paving the way to better communication

This 1866 transatlantic cable paved the way for a rapid development of telegraph communications between continents. By the end of the 1880s, some 115 000 nautical miles (213 000 km) of undersea cables had been laid. The total reached 200 000 miles (370 000 km) in 1907 and over 329 000 miles (595 000 km) in 1914.

Transatlantic cables were used only for telegraph services until 1956, when the first underwater telephone service between Europe and North America was launched. It could initially carry 36 phone channels.

The first transatlantic fibre-optic cable, which could carry 40 000 channels, entered service in 1988.

The capacity of undersea cables has increased to such an extent that it is no longer classified by the number of channels carried but by data rate, that is gigabits or terabits per second (Gbps and Tbps).

Global real-time exchange of voice and data now taken for granted

The latest transatlantic telecommunications cable, AEConnect Cable System, a 5 500 km fibre-optic cable laid from New York to Ireland, went into service in January 2016. AEConnect says that the cable “will initially support 13 Tbps (130 x 100 Gbps) per fibre pair”. This 13 Tbps data rate is equivalent to transmitting 350 DVDs worth of data in a single second. AEConnect also indicates that this capacity will continue to increase “with the introduction of more advanced modulations”. AEConnect adds that this cable will offer “one of the lowest latency crossings of the Atlantic, projected at a speed of 53,9 milliseconds”.

This represents a quantum leap from the eight words per minute the first transatlantic cable could transmit and the total time it took to decipher and forward a message.

This great technical feat, often compared to the landing on the Moon, would have been impossible to achieve at the time without the theoretical and practical work done by Lord Kelvin, which covered so many aspects of the project.

Today’s undersea communications and power cables include elements that were developed for the first transatlantic cable, including better armouring and insulation to protect the conductors from water ingress and mechanical and friction damage and rupture.

Submarine power cables were introduced much later than their telegraphic counterparts, owing to the far more complex technical issues involved.

A number of IEC Technical Committees (TCs) and Subcommittees (SCs) continue the work started by Lord Kelvin, developing a number of International Standards necessary to the production and operation of undersea power and communication cables. They include:

IEC SC 18A: Electric cables for ships and fixed offshore units, which brings together technical experts from 31 countries to prepare standards for testing methods or the production of certain elements such as cable sheathing and insulation;

IEC TC 20: Electrical cables, which prepares International Standards for the design, testing and end-use recommendations (including current ratings) for insulated electrical power and control cables, their accessories and cable systems for use in wiring and in power generation, distribution and transmission;

IEC TC 86: Fibre optics, which prepares standards for cables used to transmit data and voice, which are increasingly widely deployed in submarine environments;

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